In a conventional enclosed power transmission system, positioned inside the tubular enclosure is a first antenna element, which belongs to a control and monitoring system located outside the enclosure. This first antenna element communicates with a further antenna element located farther away within the system. The first and/or second antenna element can also communicate with sensors designed, for example, as surface wave sensors to each of which a transmitting and receiving means, for example a radio antenna, is assigned (See, e.g., International Patent Application No. 97/28587).
Another conventional method for detecting partial discharges in an enclosed, gas-insulated high-voltage system is to remove the electromagnetic waves produced as a result of partial discharges via a slot located in the enclosure, with the two conductors of a coaxial cable being connected directly to the side edges of this slot (See, e.g., European Patent No. 621 489, FIG. 10).